Nitrophenylacetic acids and derivatives as selective herbicides



United States Patent ABSTRACT OF THE DISCLOSURE.

Weeds are combated by herbicidally effective amounts of isomeric nitrophenylacetic acids and with pre-emergent control, in particular, obtained by use of 2-nitrophenylacetic acid and amides and esters thereof.

SUMMARY OF INVENTION Agricultural methods are at present undergoing revolutionary changes which feature reduction of tillage and cultivation, crowded planting of new varieties of crop plants increased use of fertilizer and chemical control of Weeds and other pests, with resulting reductionof labor I and increase of yields. It has become necessary to develop new chemical weed control techniques to suit the new methods, for several reasons. Certain species of weeds now present more serious problems because they thrive on the increased application of fertilizer and less frequent cultivation. (The term weeds as used herein refers broadly to unwanted vegetation.) Control of weeds has become more necessary because they afiect yields more seriously in crowded plantings and are a nuisance in mechanized harvesting. Chemical weed control methods must often be specially suited to the situation which exists in the field at only one particular stage of development of both crop and weeds because the farmer will only be able to make one pass through each field. Often the control technique must be aimed only at weeds which have not yet emerged, or only to those which are standing, "or to a particularly noxious species. Frequently the herbicide is required to be compatible with other chemical agents which are applied simultaneously for. other purposes. There is a need for a much greater variety of herbicides with varying selectivity, as well as compatibility so as to give farmers more freedom of choice of chemical weed control methods.

It has been discovered that nitrophenylacetic acids and derivatives possess selective herbicidal activity. An unpurified mixture of 2-, 3- and 4-nitropheny1acetic acids is particularly useful in overall weed control because it possesses considerable phytotoxic activity, both preeme rgent and post-emergent. The activity of the isomers is different, however; that of the 4-nitro compound being principally post-emergent, whereas both pie-emergent and post-emergent effects are exhibited by 2-nitroand 3-nitrophenylacetic acid. Certain derivatives of these acids are more active than the acids themselves and possess useful selectivity as well. In the method of this invention one applies to the locus of the Weeds a herbicidally effective amount of a compound represented by the structural formula:

in which X is selected from CH H and -Cl and Y is selected from the group consisting of OH, OCHg, OC2H5, --NH2 and NHOH. The method is particularly useful in standing crops such as oats, corn (Zea mays) and grain sorghum for pre-emergent control of weeds.

DETAILED DESCRIPTION OF INVENTION The isomeric nitrophenylacetic acids are known. The lower alkyl esters and amides of these acids may be made by conventional procedures. However, some of the compositions which may be employed in the weed control method are novel. Laboratory procedures which may be used to prepare the novel 2-chloroethyl esters and an unusual type of N-substituted amide are presented below for purposes of illustration.

(A) Ester synthesis Into a m1. round-bottomed flask fitted with stirrer and reflux condenser was charged 9.05 g. (0.05 mole) of 2-nitrophenylacetic acid, 100 ml. of 2-chloroethanol and 3 ml. of sulfuric acid. The reaction mixture was stirred and heated to reflux temperature for 2 hours.

The reaction mixture was cooled and was extracted with two 100 ml. portions of water. The water was extracted with 100 ml. of ether. The ether extract was concentrated by evaporation and was then poured into cold hexane to precipitate the product. The product recovered from the ether extract in a total yield of 9.1 g. was 2-chloroethyl 2-nitrophenylacetate, M.P. 58-60 C. A 2.0 gram example was recrystallized for analytical purposes (M.P. 6l-62.5 C.). The results of analysis were as follows:

Calcd. for ClNO C H (percent): CI, 14.55; N, 5.74; O, 26.27; C, 49.30; H, 4.14. Found (percent): C1, 14.37; N, 6.25; C, 49.65; H, 4.84.

(B) Hydroxy-amidation of an ester A solution of 6.9 g. of hydroxylamine in 45 ml. of methanol was prepared. To this was added a solution of 8.4 g. of potassium hydroxide in 21 ml. of methanol, with cooling. This mixture was permitted to stand at room temperature for 5 minutes. To the mixture was added 11.5 g. of ethyl 2-nitrophenylacetate dissolved in i Q0 21...... m6 -3m QM QM Q Q g QM Q Q QM 5 Q Q 560 0 "mo 3 Q2 6 Qw -25 o a Q Q H2 H2 H2 Q Q Q2 Q2 H2 H2 5o 04H mm Qc 6 QM QM QM E 3 QM QM QM QM 3 Q Q 2m mo w fio 5 Q Q Q Q Q Q Q Hz No Q Q o E Qz QwQm 5o oz HHHHHP -...----..HHH MM: QM :W Mm 8 M :MM :mw :mm :mw MM. 2m

moo mo QZ QZ Q *2 3 +2 3 HZ *2 ma, 5 No f NZ Qz E Q2 Q2 o 5% M QM QM 5 No Q Q Q Q0 3 mo 3 QM QM mow fio Q2 Q Q *2 5 E Q Q *2 E E 5 Wii o Hz 3 Hz 6 "oz 8 b .ENM QM .WM 1 m b NM: W V 1 1. -.Q.--.:.... Q Q Q Q Q Q Q :Q.HHHHHHHHHHHHHHHHHHY-.-l w oz QM QM QM No No QM QM QM QM mo QM QMW m oow fio g 5 Q Q 5 Q *2 Q Q 5 Q2 5 Q o Hz Hz Hz NZ 6 ---..-.-.-.--.-.2-HHHHH i Q Q- Q Q Q Q Q 2Q- 1b :QM i NQQ EQ O ZS 5 *2 Nm 5 Q2 Q2 No *2 Q Q2 Q2 8 Q2 Q2 Q2 Qz Q2 53 o 5 r oz 3 3 no No Na QM 8 mm mm mm QM QM::--- QM Q Q QM QM QM Q0 mooflmo Q a mm mm *2 E E mm a E a E 3 mm 5 Q6 Q0 8 No 25 o Bdnww 32B QQQM Guam :QEQM warm F60 3x0 wnwn E530 cnmnhom 52 $53M 0.96880 $3380 Q93. E QE w What is claimed is:

1. The method of combating weeds which comprises applying pre-emergently to the locus of the weeds a herbicidally effective amount of N hydroxy 2 nitrophenylacetamide.

2. The method of combating weeds which comprises applying pre-emergently to the locus of the weeds a herbicidally effective amount of 2-chloroethyl 2-nitrophenylacetate.

References Cited UNITED STATES PATENTS 3,009,806 11/1961 Weil 71-115 2,394,916 2/1946 Jones 7ll07 2,341,868 2/1944 Hitchcock et a1 71-107 OTHER REFERENCES Relation Between Molecular Structure and Physiological Activity of Plant Growth Regulators, Weintraub et al. Chem. Abs. vol. 46 (1952), 5773g.

m-Nitro and m-Trifiuoromethylaryl Acids as Plant Growth Regulators, Takeda. Chem. Abs. vol. 53 (1959), 20641f.

First Contribution to the Knowledge of the Cytological and Physiological Activity of Growth Substances in Allium Cepsa, DAmato et a1. Chem. Abs. vol. 45 (1951), 6247b.

LEWIS GOTTS, Primary Examiner C. L. MILLS, Assistant Examiner US. Cl. X.R. 

